The cumulative frequency table shows the marks of 50 students in a test. How many students scored 30 or more but less than 40?

**Less-than ogive**: plot points (upper limit of class, cf) for each class. Connect with smooth curve.

**More-than ogive**: plot points (lower limit of class, more-than-cf). Connect smoothly.

**Median from ogives**:
- Method A: From the less-than ogive, find where cf = $n/2$. Drop perpendicular to $x$-axis. The $x$-coordinate is the median.
- Method B: Plot BOTH ogives on the same axes. Their intersection's $x$-coordinate is the median.

**Empirical relationship** (rough): Mode ≈ 3 × Median − 2 × Mean. Useful sanity check, not rigorously true but often close.

**Frequency polygon vs ogive**: Polygon plots (class mark, frequency); Ogive plots (limit, cumulative frequency).